C-Band

watty

I bought a C-Band LNBF with a scalar rings feed

It has two F-Connectors
"C Band dual feed LNB freq 3.7 - 4.2"

Model DBF CH022

Is it H/V like a Universal Ku? no Co-rotator needed? 13V/18V polarity switching?

Looks a little like

except the two f-connectors underneath and not at back.


What is significance of .34, .36, .38, .40, .42 markings along the barrel? The Scalar ring bit presumably slides on the waveguide barrel and tightens up with two lock screws. Is it for different F/D dishes? Normal Ku offset dishes are about 0.6. I'm fairly sure mu Andrews /Channel master is nothing like 0.6 and the mesh dish could be anything. Peak the signal?



Will I get much on
a) A 95cm Andrews Channelmaster?
b) a 1.7m mesh dish

FTA:
which sat for Analogue?
which for Digital?

Zaphod

watty wrote:

Is it H/V like a Universal Ku? no Co-rotator needed? 13V/18V polarity switching?

Yes, integrated LNBF with 13/18V switching. Pop off the lid and you'll see the two probes at right angles.

Polarotor and corotor setups come as separate feedhorn and WR225 LNBs.

watty wrote:

What is significance of .34, .36, .38, .40, .42 markings along the barrel? The Scalar ring bit presumably slides on the waveguide barrel and tightens up with two lock screws. Is it for different F/D dishes?

The scalar rings act like blinkers and alter the dish illumination. Set to f/D ratio of dish.
http://www.geo-orbit.org/sizepgs/tuningp4.html
http://www.mlesat.com/Article1.html

Concentric sclar rings are for prime dishes f/D of .28-.42.
Conical scalar rings (rare for C-Band) for offset dishes f/D of .6-.8
http://www.mlesat.com/install.html
http://www.chaparral.net/support/trouble/feedhorn.html

watty wrote:

Will I get much on
a) A 95cm Andrews Channelmaster?
b) a 1.7m mesh dish

FTA:
which sat for Analogue?
which for Digital?

I got 26e analogue and digital on an 80cm Lidl, so the 95cm should be a bit better. 58W has strong digital signals too. OK for messing but the 1.7m dish will be much more useful.

Most signals are RHCP/LHCP so you need to source a dielectric insert at some stage - makes a difference of about 3dB.

Very little on C-band on English language European forums. German DXTV is good though. Lots of people experimenting with ~1M dishes.
http://forum.dxtv.de/wbb/hmportal.php

watty

I was think you might answer. Thanks.

Confirms mostly what I thought. I had forgotten about the circular polarisation. Is it just a disc of teflon or chopping board? what position does it go at. Or two different positions for LH & RH?

A few frequencies use RH & LH on same frequency, so I imagine that won't work at all without the dielectric converter.


Thanks Zaphod.

Zaphod

Usually teflon. For optimum results both the type of material and the size/shape of the insert will affect signal strength/quality.

Hard to give a definitive answer on discrimination between RHCP/LHCP without insert - in theory no, in practice maybe.

Insert goes at 45 degree angles to H/V probes.

watty

The Channel master is a Vsat dish, so much less offset and VERY heavy arm and lower f/D I think...

Do I mount the scaler rings at focus and slide the LNB tube for F/D?

The Mesh dish is missing the centre part that all the ribs bolt too. The guy I'm getting it off has it somewhere. He also has a similar 3.4m petal mesh dish, never used and elevation and azimuth actuators. That he will get me to help him install. It will be at ground level in his 8 acre field.

watty

Actually since there is a set of DIP switches to use one or two QUAD instead of Quattro LNBs on the Multiswitch, a single sat position set of 4 inputs on the Multiswitch can connect to a Dual or Twin C-band LNBF, or possibly a pair of Dual or Twin LNBFs if you can define 22kHz on as separate 5th position on the receiver menu.

Zaphod

The firsk URL above explains it all. Set scaler according to f/D first and then measure focal point to the internal probe(s). For an offset dish, results may be better with no scalars - that's what I found with 80cm dish.

watty

Thanks.
Awkward since mount holes on scaler ring. Oddly the blue front cover is not water tight. Holes all the way round.